This fast track grant titled, Low Dose Rapid Scanning Slit Digital Mammography and Breast Tomosynthesis will enable us to bring to market a clinically driven improved method of breast imaging based on photon-counting x-ray detector arrays with energy discrimination. The detectors will enabled significant improvements in x-ray breast imaging such as reduced patient dose while maintaining excellent image quality, enhanced tissue contrast, material decomposition capabilities (tissue type identification), and quantitative iodine contrast imaging. The overall goal is to bring to the marketplace a photon-counting energy-dispersive x-ray detector with energy discrimination for use in human breast imaging. So far we have demonstrated a first generation fast photon-counting x-ray imaging array prototype which has a higher maximum output count rate (by more than an order of magnitude) than all others, and the array has been used to generate the preliminary data. Our technology is capable of counting at over 1 106 counts per second (cps) per 100 m pixel which is 1 108 cps/mm2 and is the highest output count rate (OCR) measured to date with x-rays to our knowledge. Our x-ray imaging arrays are completely vertically integrated and can be tiled to large field of view. We use this technology to develop scanning slit breast imaging with multiple stacked 1D high flux energy resolved single photon counting detector arrays. For scanning slit digital mammography (DM) we have the advantage of energy information as compared to the currently available systems. Whereas for scanning slit digital breast tomosynthesis (DBT) we would have, in addition to energy information, scatter rejection from the multi-slit scanning. Building a system capable of both DM and DBT in a scanning slit mode offers the chance to achieve DM, DBT, and synthetic DM from DBT data all on one system. A gantry design will be used to sweep the detector slits across the FOV always close to and parallel to the compressed breast and always pointing to the focal spot for both DM (tube at 0) and DBT (tube anywhere between 25) so that the geometry of the projection images is the same as currently used in flat panel DM and BDT. The high OCR allows the use of a strong 50 mA x-ray tube to produce shorter scan times. The proposed photon counting x-ray detector based breast imaging will not only improve the quality of the current attenuation-based gray-scale images, but also open a door to completely new applications, new procedures, and new protocols, using the capabilities of tissue-type specific x-ray images. We expect large commercial success with this product. This is due to the significant improvements to and advantages over existing detectors that our technology provides together with the widespread and increasing use of breast imaging. The x-ray exposure in breast cancer screening has been of major concern for radiologists and physicists as the number of examinations has increased. Therefore, a method which reduces the patient dose in screening examinations will have a significant impact on public health. Our product addresses the need to reduce dose in breast imaging. At the same time, improved tissue differentiation and contrast specific identification is needed for better diagnosis. Our product addresses these needs by improving image quality by making use of the energy information contained in the individually counted x-rays at high flux, information that is currently not obtainable with the non photon-counting x-ray imaging arrays currently in use in breast imaging systems.